Many medical procedures require repeated and prolonged access to a patient's vasculature for the delivery and/or exchange of drugs, blood products, nutritional fluids, or other fluids. Medical devices such as peripherally inserted catheters (PICCs), dialysis catheters, tunneled central catheters and subcutaneously implanted ports have been developed to ensure that a patient's peripheral vasculature does not sustain damage from repeated access. These long-term devices remain inserted in the patient's central vasculature for the duration of treatment protocols, which may last weeks, months or even years. It is medically desirable to manage fluid exchanges through these devices by controlling the fluid flow to prevent device complications such as fluid leakage and blood clotting. Clamps attached to the catheter shaft or extension tubing of the vascular access device have been employed to close of the fluid pathway when not in use. Using clamps has been shown to be problematic because the repeated pressure of the clamp against the tubing wall may weaken and damage the device tubing. Another problem with clamps the possibility of an incomplete tubing seal, which may result in the introduction of air into the fluid path and/or blood coagulation.
Based on the problems associated with clamps, bi-directional, pressure-activated valve assemblies have been incorporated into medical devices to provide required fluid flow control. These bi-directional, pressure-actuated valves generally include an elastic diaphragm or disk positioned within the device's fluid flow path that controls fluid flow through the device. The elastic diaphragm prevents inadvertent fluid flow when the device is not being used. The diaphragm may be a slitted, flexible membrane extending across a lumen, and generally constructed so that, when subjected to a fluid pressure of at least a threshold level, the edges of the slit separate from one another to form an opening through which fluid flows. When the pressure applied to the membrane drops below a predetermined threshold level, the slit closes to prevent fluid flow from or into the device. One such bi-directional, pressure-actuated valve assembly is described in U.S. Pat. No. 7,435,236 entitled Pressure-Actuated Valve with Improved Biasing Member, which is incorporated herein by reference.
One known design of a bi-directional, flexible diaphragm requires that the fluid pass through the same slit during both aspiration and infusion. The cracking pressure of such an elastic diaphragm is determined by the geometry of the valve housing components and how they mate with the peripheral part of the disk. A cracking pressure may be defined as the threshold pressure at which a fluid flow control portion of the diaphragm permits fluid to flow through the diaphragm. Thus, any adjustment of the fluid flow control portion, such as dimensions and slit geometry, influences fluid flow in both the injection and aspiration directions. Since it may be clinically desirable to have different cracking pressures for aspiration and injection, the design of the hub or other component which houses the disk must be dimensioned to account for two separate pressure differentials. Accordingly, there is a need for an improved bi-directional, pressure-actuated valve assembly having an elastic diaphragm that provides separate and independent injection and aspiration functions, each with unique cracking pressure.
Yet another problem with prior art pressure-actuated diaphragms is the increased probability of hemolysis during aspiration or infusion of blood. Hemolysis is the mechanical rupturing of red blood cells (erythrocytes) which causes the release of hemoglobin into the patient's circulatory system. Extracellular or “free” hemoglobin has been found to be associated with acute and chronic vascular disease, inflammation, thrombosis, renal impairment and other serious medical complications. Aspirating and infusing blood through a bi-directional slit valve results in shear forces and turbulence that may mechanically damage the erythrocytes and cause hemolysis. More particularly, as the blood is forced through the narrow slit of the diaphragm, the red erythrocytes are ruptured by the sharp edges of the slit. Accordingly, there is a need for a pressure-actuated, bi-directional valve assembly which minimizes the occurrence of hemolysis during blood infusion and aspiration.
Known methods of manufacturing an elastic diaphragm and housing assembly may be problematic, and result in high scrap rates. Typically, the valve is formed from a silicone sheet material which is punched to form the diaphragm with slit. The sheet material thickness and elastic modulus, both critical specifications to ensuring proper cracking pressures, are often inconsistent and may vary even within a single sheet. To address this problem, the sheet material undergoes a customized annealing process prior to punching the disks from the sheet. Due to the natural stretching of the disk material after assembly, the finished valve assembly is once again annealed to achieve the desired pressure actuation thresholds. These additional manufacturing and quality control steps result in a high scrap rate, long manufacturing cycles, inefficient production resource utilization and may have a negative impact on production responsiveness. Accordingly, there is a need for an improved valve assembly design which streamlines and shortens the manufacturing process, increases production throughput and more efficiently utilizes production resources.